Yeah, I can see Ufotable fitting in some of Saber's character development from the Fate route so that her character arc from Zero will get a conclusion and, despite not being the Main Heroine or Shirou's love interest, so that she'll still get a decent amount of focus in the anime.
I wonder if that might also somewhat extend to Illya as well? Especially considering her ultimate fate in UBW.
There's no way to tell as of now. Ilya doesn't get a lot of focus in UBW, so it'd be hard for the staff to pack in some Ilya-centric stuff to give her a proper conclusion, unless they were to make serious alterations to the UBW story which is something I'm suspecting they will do. At least in Saber's case they can rearrange her character development around various UBW events because Saber's always in the middle of the action even though she isn't the "focus" character like Rin is.
But I am not sure that this UBW adaptation will be as "straight" as people assume it will be. They can't do a straight adaptation, none of the Fate storylines are long enough to support 24-26 episodes. There will be alterations made, and as the Heaven's Feel movie is being produced I think that while UBW will be the "main" route, they will fit in as much of the Fate route as they can (both for padding and to give Saber a proper conclusion) and also throw a original spin onto things to make everything work. What that means for Saber and Ilya I don't know, but I don't think either character will conclude this adaptation of UBW the way their paths concluded in the game or in the DEEN adaptation.
It's sort of like the way the official Fate/stay night manga is handled. The UBW route is the base but the manga carefully fits in elements of the other routes and also has its own original direction that makes the manga unique in its own way. While I don't think this anime will adapt the manga one iota, I think the same principle will apply here.
